-----------------------------------------------------------------------------  
-- JSON4Lua: JSON encoding / decoding support for the Lua language.  
-- json Module.  
-- Author: Craig Mason-Jones  
-- Homepage: http://json.luaforge.net/  
-- Version: 0.9.40  
-- This module is released under the MIT License (MIT).  
-- Please see LICENCE.txt for details.  
--  
-- USAGE:  
-- This module exposes two functions:  
--   encode(o)  
--     Returns the table / string / boolean / number / nil / json.null value as a JSON-encoded string.  
--   decode(json_string)  
--     Returns a Lua object populated with the data encoded in the JSON string json_string.  
--  
-- REQUIREMENTS:  
--   compat-5.1 if using Lua 5.0  
--  
-- CHANGELOG  
--   0.9.20 Introduction of local Lua functions for private functions (removed _ function prefix).   
--          Fixed Lua 5.1 compatibility issues.  
--          Introduced json.null to have null values in associative arrays.  
--          encode() performance improvement (more than 50%) through table.concat rather than ..  
--          Introduced decode ability to ignore /**/ comments in the JSON string.  
--   0.9.10 Fix to array encoding / decoding to correctly manage nil/null values in arrays.  
-----------------------------------------------------------------------------  
  
-----------------------------------------------------------------------------  
-- Imports and dependencies  
-----------------------------------------------------------------------------  
local math = require('math')  
local string = require("string")  
local table = require("table")  
  
local base = _G  
  
-----------------------------------------------------------------------------  
-- Module declaration  
-----------------------------------------------------------------------------  
-- module("json")  
local json = {}
  
-- Public functions  
  
-- Private functions  
local decode_scanArray  
local decode_scanComment  
local decode_scanConstant  
local decode_scanNumber  
local decode_scanObject  
local decode_scanString  
local decode_scanWhitespace  
local encodeString  
local isArray  
local isEncodable  
  
-----------------------------------------------------------------------------  
-- PUBLIC FUNCTIONS  
-----------------------------------------------------------------------------  
--- Encodes an arbitrary Lua object / variable.  
-- @param v The Lua object / variable to be JSON encoded.  
-- @return String containing the JSON encoding in internal Lua string format (i.e. not unicode)  
function json.encode (v)  
  -- Handle nil values  
  if v==nil then  
    return "null"  
  end  
    
  local vtype = base.type(v)    
  
  -- Handle strings  
  if vtype=='string' then      
    return '"' .. encodeString(v) .. '"'        -- Need to handle encoding in string  
  end  
    
  -- Handle booleans  
  if vtype=='number' or vtype=='boolean' then  
    return base.tostring(v)  
  end  
    
  -- Handle tables  
  if vtype=='table' then  
    local rval = {}  
    -- Consider arrays separately  
    local bArray, maxCount = isArray(v)  
    if bArray then  
      for i = 1,maxCount do  
        table.insert(rval, json.encode(v[i]))  
      end  
    else    -- An object, not an array  
      for i,j in base.pairs(v) do  
        if isEncodable(i) and isEncodable(j) then  
          table.insert(rval, '"' .. encodeString(i) .. '":' .. json.encode(j))  
        end  
      end  
    end  
    if bArray then  
      return '[' .. table.concat(rval,',') ..']'  
    else  
      return '{' .. table.concat(rval,',') .. '}'  
    end  
  end  
    
  -- Handle null values  
  if vtype=='function' and v==null then  
    return 'null'  
  end  
    
  base.assert(false,'encode attempt to encode unsupported type ' .. vtype .. ':' .. base.tostring(v))  
end  
  
  
--- Decodes a JSON string and returns the decoded value as a Lua data structure / value.  
-- @param s The string to scan.  
-- @param [startPos] Optional starting position where the JSON string is located. Defaults to 1.  
-- @param Lua object, number The object that was scanned, as a Lua table / string / number / boolean or nil,  
-- and the position of the first character after  
-- the scanned JSON object.  
function json.decode(s, startPos)  
  startPos = startPos and startPos or 1  
  startPos = decode_scanWhitespace(s,startPos)  
  base.assert(startPos<=string.len(s), 'Unterminated JSON encoded object found at position in [' .. s .. ']')  
  local curChar = string.sub(s,startPos,startPos)  
  -- Object  
  if curChar=='{' then  
    return decode_scanObject(s,startPos)  
  end  
  -- Array  
  if curChar=='[' then  
    return decode_scanArray(s,startPos)  
  end  
  -- Number  
  if string.find("+-0123456789.e", curChar, 1, true) then  
    return decode_scanNumber(s,startPos)  
  end  
  -- String  
  if curChar==[["]] or curChar==[[']] then  
    return decode_scanString(s,startPos)  
  end  
  if string.sub(s,startPos,startPos+1)=='/*' then  
    return decode(s, decode_scanComment(s,startPos))  
  end  
  -- Otherwise, it must be a constant  
  return decode_scanConstant(s,startPos)  
end  
  
--- The null function allows one to specify a null value in an associative array (which is otherwise  
-- discarded if you set the value with 'nil' in Lua. Simply set t = { first=json.null }  
function null()  
  return null -- so json.null() will also return null ;-)  
end  
-----------------------------------------------------------------------------  
-- Internal, PRIVATE functions.  
-- Following a Python-like convention, I have prefixed all these 'PRIVATE'  
-- functions with an underscore.  
-----------------------------------------------------------------------------  
  
--- Scans an array from JSON into a Lua object  
-- startPos begins at the start of the array.  
-- Returns the array and the next starting position  
-- @param s The string being scanned.  
-- @param startPos The starting position for the scan.  
-- @return table, int The scanned array as a table, and the position of the next character to scan.  
function decode_scanArray(s,startPos)  
  local array = {}  -- The return value  
  local stringLen = string.len(s)  
  base.assert(string.sub(s,startPos,startPos)=='[','decode_scanArray called but array does not start at position ' .. startPos .. ' in string:\n'..s )  
  startPos = startPos + 1  
  -- Infinite loop for array elements  
  repeat  
    startPos = decode_scanWhitespace(s,startPos)  
    base.assert(startPos<=stringLen,'JSON String ended unexpectedly scanning array.')  
    local curChar = string.sub(s,startPos,startPos)  
    if (curChar==']') then  
      return array, startPos+1  
    end  
    if (curChar==',') then  
      startPos = decode_scanWhitespace(s,startPos+1)  
    end  
    base.assert(startPos<=stringLen, 'JSON String ended unexpectedly scanning array.')  
    object, startPos = json.decode(s,startPos)  
    table.insert(array,object)  
  until false  
end  
  
--- Scans a comment and discards the comment.  
-- Returns the position of the next character following the comment.  
-- @param string s The JSON string to scan.  
-- @param int startPos The starting position of the comment  
function decode_scanComment(s, startPos)  
  base.assert( string.sub(s,startPos,startPos+1)=='/*', "decode_scanComment called but comment does not start at position " .. startPos)  
  local endPos = string.find(s,'*/',startPos+2)  
  base.assert(endPos~=nil, "Unterminated comment in string at " .. startPos)  
  return endPos+2    
end  
  
--- Scans for given constants: true, false or null  
-- Returns the appropriate Lua type, and the position of the next character to read.  
-- @param s The string being scanned.  
-- @param startPos The position in the string at which to start scanning.  
-- @return object, int The object (true, false or nil) and the position at which the next character should be   
-- scanned.  
function decode_scanConstant(s, startPos)  
  local consts = { ["true"] = true, ["false"] = false, ["null"] = nil }  
  local constNames = {"true","false","null"}  
  
  for i,k in base.pairs(constNames) do  
    --print ("[" .. string.sub(s,startPos, startPos + string.len(k) -1) .."]", k)  
    if string.sub(s,startPos, startPos + string.len(k) -1 )==k then  
      return consts[k], startPos + string.len(k)  
    end  
  end  
  base.assert(nil, 'Failed to scan constant from string ' .. s .. ' at starting position ' .. startPos)  
end  
  
--- Scans a number from the JSON encoded string.  
-- (in fact, also is able to scan numeric +- eqns, which is not  
-- in the JSON spec.)  
-- Returns the number, and the position of the next character  
-- after the number.  
-- @param s The string being scanned.  
-- @param startPos The position at which to start scanning.  
-- @return number, int The extracted number and the position of the next character to scan.  
function decode_scanNumber(s,startPos)  
  local endPos = startPos+1  
  local stringLen = string.len(s)  
  local acceptableChars = "+-0123456789.e"  
  while (string.find(acceptableChars, string.sub(s,endPos,endPos), 1, true)  
    and endPos<=stringLen  
    ) do  
    endPos = endPos + 1  
  end  
  local stringValue = 'return ' .. string.sub(s,startPos, endPos-1)  
  -- print(stringValue)
  -- local stringEval = base.loadstring(stringValue)  
  local stringEval = function ()
      return tonumber(string.sub(s,startPos, endPos-1))  
  end
  base.assert(stringEval, 'Failed to scan number [ ' .. stringValue .. '] in JSON string at position ' .. startPos .. ' : ' .. endPos)  
  return stringEval(), endPos  
end  
  
--- Scans a JSON object into a Lua object.  
-- startPos begins at the start of the object.  
-- Returns the object and the next starting position.  
-- @param s The string being scanned.  
-- @param startPos The starting position of the scan.  
-- @return table, int The scanned object as a table and the position of the next character to scan.  
function decode_scanObject(s,startPos)  
  local object = {}  
  local stringLen = string.len(s)  
  local key, value  
  base.assert(string.sub(s,startPos,startPos)=='{','decode_scanObject called but object does not start at position ' .. startPos .. ' in string:\n' .. s)  
  startPos = startPos + 1  
  repeat  
    startPos = decode_scanWhitespace(s,startPos)  
    base.assert(startPos<=stringLen, 'JSON string ended unexpectedly while scanning object.')  
    local curChar = string.sub(s,startPos,startPos)  
    if (curChar=='}') then  
      return object,startPos+1  
    end  
    if (curChar==',') then  
      startPos = decode_scanWhitespace(s,startPos+1)  
    end  
    base.assert(startPos<=stringLen, 'JSON string ended unexpectedly scanning object.')  
    -- Scan the key  
    key, startPos = json.decode(s,startPos)  
    base.assert(startPos<=stringLen, 'JSON string ended unexpectedly searching for value of key ' .. key)  
    startPos = decode_scanWhitespace(s,startPos)  
    base.assert(startPos<=stringLen, 'JSON string ended unexpectedly searching for value of key ' .. key)  
    base.assert(string.sub(s,startPos,startPos)==':','JSON object key-value assignment mal-formed at ' .. startPos)  
    startPos = decode_scanWhitespace(s,startPos+1)  
    base.assert(startPos<=stringLen, 'JSON string ended unexpectedly searching for value of key ' .. key)  
    value, startPos = json.decode(s,startPos)  
    object[key]=value  
  until false   -- infinite loop while key-value pairs are found  
end  
  
-- START SoniEx2  
-- Initialize some things used by decode_scanString  
-- You know, for efficiency  
local escapeSequences = {  
  ["\\t"] = "\t",  
  ["\\f"] = "\f",  
  ["\\r"] = "\r",  
  ["\\n"] = "\n",  
  ["\\b"] = "\b"  
}  
base.setmetatable(escapeSequences, {__index = function(t,k)  
  -- skip "\" aka strip escape  
  return string.sub(k,2)  
end})  
-- END SoniEx2  
  
--- Scans a JSON string from the opening inverted comma or single quote to the  
-- end of the string.  
-- Returns the string extracted as a Lua string,  
-- and the position of the next non-string character  
-- (after the closing inverted comma or single quote).  
-- @param s The string being scanned.  
-- @param startPos The starting position of the scan.  
-- @return string, int The extracted string as a Lua string, and the next character to parse.  
function decode_scanString(s,startPos)  
  base.assert(startPos, 'decode_scanString(..) called without start position')  
  local startChar = string.sub(s,startPos,startPos)  
  -- START SoniEx2  
  -- PS: I don't think single quotes are valid JSON  
  base.assert(startChar == [["]] or startChar == [[']],'decode_scanString called for a non-string')  
  --base.assert(startPos, "String decoding failed: missing closing " .. startChar .. " for string at position " .. oldStart)  
  local t = {}  
  local i,j = startPos,startPos  
  while string.find(s, startChar, j+1) ~= j+1 do  
    local oldj = j  
    i,j = string.find(s, "\\.", j+1)  
    local x,y = string.find(s, startChar, oldj+1)  
    if not i or x < i then  
      -- base.print(s, startPos, string.sub(s,startPos,oldj))  
      i,j = x,y-1  
      if not x then base.print(s, startPos, string.sub(s,startPos,oldj)) end  
    end  
    table.insert(t, string.sub(s, oldj+1, i-1))  
    if string.sub(s, i, j) == "\\u" then  
      local a = string.sub(s,j+1,j+4)  
      j = j + 4  
      local n = base.tonumber(a, 16)  
      base.assert(n, "String decoding failed: bad Unicode escape " .. a .. " at position " .. i .. " : " .. j)  
      -- math.floor(x/2^y) == lazy right shift  
      -- a % 2^b == bitwise_and(a, (2^b)-1)  
      -- 64 = 2^6  
      -- 4096 = 2^12 (or 2^6 * 2^6)  
      local x  
      if n < 0x80 then  
        x = string.char(n % 0x80)  
      elseif n < 0x800 then  
        -- [110x xxxx] [10xx xxxx]  
        x = string.char(0xC0 + (math.floor(n/64) % 0x20), 0x80 + (n % 0x40))  
      else  
        -- [1110 xxxx] [10xx xxxx] [10xx xxxx]  
        x = string.char(0xE0 + (math.floor(n/4096) % 0x10), 0x80 + (math.floor(n/64) % 0x40), 0x80 + (n % 0x40))  
      end  
      table.insert(t, x)  
    else  
      table.insert(t, escapeSequences[string.sub(s, i, j)])  
    end  
  end  
  table.insert(t,string.sub(j, j+1))  
  base.assert(string.find(s, startChar, j+1), "String decoding failed: missing closing " .. startChar .. " at position " .. j .. "(for string at position " .. startPos .. ")")  
  return table.concat(t,""), j+2  
  -- END SoniEx2  
end  
  
--- Scans a JSON string skipping all whitespace from the current start position.  
-- Returns the position of the first non-whitespace character, or nil if the whole end of string is reached.  
-- @param s The string being scanned  
-- @param startPos The starting position where we should begin removing whitespace.  
-- @return int The first position where non-whitespace was encountered, or string.len(s)+1 if the end of string  
-- was reached.  
function decode_scanWhitespace(s,startPos)  
  local whitespace=" \n\r\t"  
  local stringLen = string.len(s)  
  while ( string.find(whitespace, string.sub(s,startPos,startPos), 1, true)  and startPos <= stringLen) do  
    startPos = startPos + 1  
  end  
  return startPos  
end  
  
--- Encodes a string to be JSON-compatible.  
-- This just involves back-quoting inverted commas, back-quotes and newlines, I think ;-)  
-- @param s The string to return as a JSON encoded (i.e. backquoted string)  
-- @return The string appropriately escaped.  
  
local escapeList = {  
    ['"']  = '\\"',  
    ['\\'] = '\\\\',  
    ['/']  = '\\/',   
    ['\b'] = '\\b',  
    ['\f'] = '\\f',  
    ['\n'] = '\\n',  
    ['\r'] = '\\r',  
    ['\t'] = '\\t'  
}  
  
function encodeString(s)  
 return s:gsub(".", function(c) return escapeList[c] end) -- SoniEx2: 5.0 compat  
end  
  
-- Determines whether the given Lua type is an array or a table / dictionary.  
-- We consider any table an array if it has indexes 1..n for its n items, and no  
-- other data in the table.  
-- I think this method is currently a little 'flaky', but can't think of a good way around it yet...  
-- @param t The table to evaluate as an array  
-- @return boolean, number True if the table can be represented as an array, false otherwise. If true,  
-- the second returned value is the maximum  
-- number of indexed elements in the array.   
function isArray(t)  
  -- Next we count all the elements, ensuring that any non-indexed elements are not-encodable   
  -- (with the possible exception of 'n')  
  local maxIndex = 0  
  for k,v in base.pairs(t) do  
    if (base.type(k)=='number' and math.floor(k)==k and 1<=k) then   -- k,v is an indexed pair  
      if (not isEncodable(v)) then return false end -- All array elements must be encodable  
      maxIndex = math.max(maxIndex,k)  
    else  
      if (k=='n') then  
        if v ~= table.getn(t) then return false end  -- False if n does not hold the number of elements  
      else -- Else of (k=='n')  
        if isEncodable(v) then return false end  
      end  -- End of (k~='n')  
    end -- End of k,v not an indexed pair  
  end  -- End of loop across all pairs  
  return true, maxIndex  
end  
  
--- Determines whether the given Lua object / table / variable can be JSON encoded. The only  
-- types that are JSON encodable are: string, boolean, number, nil, table and json.null.  
-- In this implementation, all other types are ignored.  
-- @param o The object to examine.  
-- @return boolean True if the object should be JSON encoded, false if it should be ignored.  
function isEncodable(o)  
  local t = base.type(o)  
  return (t=='string' or t=='boolean' or t=='number' or t=='nil' or t=='table') or (t=='function' and o==null)   
end  

return json